The subject of the invention is a process and a device for carrying out the process of electro-erosive treatment of workpieces by wire-like or strip-like electrodes. A path of the relative movements between the workpiece and the electrode is controlled by means of an electronic control system. The wire-like or strip-like electrode is threaded by a drive and guide system from the feed side into a starting bore of the contour which is provided in the workpiece and is thrust or drawn through the starting bore until the electrode forms an active connection with a delivery side of the drive and guide system.
Wire eroding machines, in particular those controlled numerically, can be used with great advantage for cutting complicated outer or inner contours on electrically conductive workpieces. As is known, during the treatment process wire-like or strip-like electrodes and workpieces move relative to one another. The electrode is drawn off from a feed roller, moves past the workpiece which is to be treated, and passes through a drive device which consists of a pair of rollers and which provides the electrode with a uniform forwards movement. Finally the electrode is rewound onto a roller or chopped into small pieces which fall into a waste container. A sensor arranged between the feed rollers and the workpiece checks for the presence of a slight mechanical tensile stress in the electrode. If there is no tensile stress due to a disturbance, the sensor disconnects the electrical voltage which produces the erosive sparks, disconnects the numerical control system and brings the forwards movement of the electrode to a halt.
In spite of the provision of a numerical control system, commercially available erosion machines require the presence of an operator since the threading of the electrode into the starting bores in order to produce inner and outer contours necessitates manual intervention. In order to avoid this disadvantage it has already been proposed to provide a special cutting and feed device for the electrode and a mobile gripper to introduce the electrode into the transport path used for normal operation. The known threading device has the disadvantage that the threading procedure necessitates intervention in the control device since a large number of movement sequences must be executed. The known device does not operate reliably since precise setting and coordination of the fixing procedure, cutting-off procedure and feed motion is difficult. Moreover copper deposits are formed on the cutting tool resulting not only in a faulty mode of operation but also a heavy wear on the tool.